Aeronautical antenna systems for satellite communications can be very large in area, which results in increased air drag and more weight for the aircraft on which the antenna system is mounted. Increased drag and weight result in a reduction in the aircraft's flying range, increased fuel consumption and corresponding higher aircraft operational costs. Large antenna systems can also increase lightning and bird strike risks, as well as degrade the visual aesthetics of the aircraft.
Communications with satellites using physically small antenna arrays requires an exceptionally low noise temperature and high aperture efficiency. In aeronautical applications, the antenna should also be narrow and have a low profile in order to minimize drag and not deviate excessively from the contours of the aircraft. Conventional antenna systems for aeronautical satellite communications (SATCOM) applications, in the lower microwave frequency bands, typically utilize either drooping-crossed-dipole elements or microstrip patch radiators. The configuration of crossed-dipole elements is relatively tall, which results in high drag.
The microstrip patch element has a relatively low profile, but has both a narrow beamwidth and narrow bandwidth, which restrict the antenna's performance. The narrow beamwidth of the patch element results in excessive gain reduction and impedance mismatch when the array beam peak is scanned toward the aircraft horizon with the antenna mounted on the top of the fuselage. The narrow bandwidth of the patch radiator makes the impedance mismatch more catastrophic at extreme scan angles. These effects reduce the gain of the antenna system, thus requiring that the antenna have a larger antenna footprint and overall larger size.
In addition, conventional antenna arrays have beam steering systems for creating beam radiation patterns that use simple look-up tables for determining element phase settings for a given beam position relative to the airframe. This current approach to determining element phase settings does not minimize interference with other satellites on the geosynchronous arc. Consequently, the size of the antenna must be relatively large in order to achieve a desired degree of isolation against satellites other than the one with which communication is desired.
Some existing high gain phased array antenna systems for aeronautical Inmarsat applications include the CMA-2102 antenna system by CMC Electronics, the T4000 antenna system by Tecom, the HGA 7000 antenna system by Omnipless, and the Airlink and Dassault Electronique Conformal antenna system by Ball Aerospace. The CMA-2102 and Tecom T4000 antenna systems are conventional drooping crossed dipole arrays of large size that use conventional steering algorithms and conventional mounting techniques. The Omnipless HGA 7000 antenna system has not yet been sold commercially and is of unknown construction. The Ball Aerospace Airlink and Dassault Electronique conformal antenna systems are conventional microstrip patch arrays that use conventional steering algorithms and conventional mounting techniques.
A need exists for a small antenna system that can be mounted on a small surface area, and which has high gain in directions of intended communication and low interference in other directions. A need also exists for a small, compact antenna system that has high beam-steering accuracy, wide bandwidth and very efficient radiation.